$.fn.selectReadOnly=function(){	//固定select的值
    var tem=$(this).children('option').index($("option:selected"));
    $(this).change(function(){
          $(this).children('option').eq(tem).attr("selected",true); 
    });
}

//=================================截取中文字符======================================//

//计算字符串长度
String.prototype.strLen = function() {
        var len = 0;
        for (var i = 0; i < this.length; i++) {
            if (this.charCodeAt(i) > 255 || this.charCodeAt(i) < 0) len += 2;
            else len++;
        }
        return len;
    }
    //将字符串拆成字符，并存到数组中
String.prototype.strToChars = function() {
        var chars = new Array();
        for (var i = 0; i < this.length; i++) {
            chars[i] = [this.substr(i, 1), this.isCHS(i)];
        }
        String.prototype.charsArray = chars;
        return chars;
    }
    //判断某个字符是否是汉字
String.prototype.isCHS = function(i) {
        if (this.charCodeAt(i) > 255 || this.charCodeAt(i) < 0)
            return true;
        else
            return false;
    }
    //截取字符串（从start字节到end字节）
String.prototype.subCHString = function(start, end) {
        var len = 0;
        var str = "";
        this.strToChars();
        for (var i = 0; i < this.length; i++) {
            if (this.charsArray[i][1])
                len += 2;
            else
                len++;
            if (end < len)
                return str;
            else if (start < len)
                str += this.charsArray[i][0];
        }
        return str;
    }
    //截取字符串（从start字节截取length个字节）
String.prototype.subCHStr = function(start, length) {
    return this.subCHString(start, start + length);
}

//=================================截取中文字符 END======================================//


